Disclosed herein are piezoelectric ink jet printheads and methods for making them.
Ink jet systems include one or more printheads having a plurality of jets from which drops of fluid are ejected towards a recording medium. The jets of a printhead receive ink from an ink supply chamber or manifold in the printhead which, in turn, receives ink from a source, such as an ink reservoir or an ink cartridge. Each jet includes a channel having one end in fluid communication with the ink supply manifold. The other end of the ink channel has an orifice or nozzle for ejecting drops of ink. The nozzles of the jets can be formed in an aperture or nozzle plate having openings corresponding to the nozzles of the jets. During operation, drop ejecting signals activate actuators in the jets to expel drops of fluid from the jet nozzles onto the recording medium. By selectively activating the actuators of the jets to eject drops as the recording medium and/or printhead assembly are moved relative to one another, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium. An example of a full width array printhead is described in U.S. Pat. No. 7,591,535, the disclosure of which is totally incorporated herein by reference. Additional examples of ink jet printheads are disclosed in U.S. Pat. Nos. 7,934,815, 7,862,678, and 7,862,160, and in U.S. Patent Publications 2011/0175971, 2011/0141203, 2011/0141204, 2011/0141205, and 2010/0294545, the disclosures of each of which are totally incorporated herein by reference.
Piezoelectric ink jet printheads typically include a flexible diaphragm and a piezoelectric transducer attached to the diaphragm. When a voltage is applied to the piezoelectric transducer, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric transducer vibrates, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
One goal of printhead design is to provide increasing numbers of ink jet ejectors in a printhead. The more ink jet ejectors in a printhead, the greater the density of the dot matrix and the higher the perceived quality of the image. One approach to increasing ink jet ejector density in a printhead is to locate the manifold external to the ink jet ejector. One way of implementing this approach includes providing an inlet in the diaphragm layer for each ejector. Coupling the inlet to the manifold to receive ink for ejection from the ejector, however, requires an opening in the piezoelectric transducer layer to enable ink flow from the manifold to the inlet and then into the pressure chamber in the ink jet body plate. Each opening in the piezoelectric transducer layer is located in a polymer portion in the interstices between the piezoelectric transducers.
To facilitate manufacture of an ink jet array printhead, an array of ink jet ejectors can be formed from multiple laminated plates or sheets. These sheets are configured with a plurality of pressure chambers, outlets, and apertures and then stacked in a superimposed relationship. These sheets or plates include a diaphragm plate, an ink jet body plate, an inlet plate, an outlet plate, and an aperture plate. The piezoelectric-transducer is bonded to the diaphragm, which is a region of the diaphragm plate that overlies the ink pressure chamber.
Conventional approaches to assembling a high density ink jet printhead stack array include the use of a thermoset polymer to be used as an interstitial fill between the piezoelectric transducers. The polymer is planarized flat with the piezoelectric transducer array (within 5 microns) and excess polymer on top of the piezoelectric transducer array is etched away to expose clean piezoelectric transducer material for electrical connection. Further, an additional film adhesive layer, the standoff, is used to bond the top electrical connect circuitry to the array. Upon laser drilling, the thermoset polymer becomes a channel for ink flow. Potential quality issues with this method include the possibility of polymer on the top of the piezoelectric transducers, which could cause electrical connectivity issues, and potential bond degradation at the electrical connection from lack of potting material.
Accordingly, a need remains for improved methods for forming high density ink jet printhead stack arrays. In addition, a need remains for methods for making ink jet printheads with fewer layers. Further, a need remains for methods for making ink jet printheads with improved electrical connections. Additionally, a need remains for methods for making ink jet printheads in which there is no need to planarize the polymer with the top of the piezoelectric transducer layer and no need for a post-planarization etching process, thereby eliminating extra processing equipment and steps.